Academic Unit of Clinical & Experimental Sciences, Faculty of Medicine, University of Southampton, Southampton, UK.
Eur J Immunol. 2012 Jan;42(1):248-55. doi: 10.1002/eji.201141956. Epub 2011 Nov 28.
Human invariant natural killer T (NKT) cell TCRs bind to CD1d via an "invariant" Vα24-Jα18 chain (iNKTα) paired to semi-invariant Vβ11 chains (iNKTβ). Single-amino acid variations at position 93 (p93) of iNKTα, immediately upstream of the "invariant" CDR3α region, have been reported in a substantial proportion of human iNKT-cell clones (4-30%). Although p93, a serine in most human iNKT-cell TCRs, makes no contact with CD1d, it could affect CD1d binding by altering the conformation of the crucial CDR3α loop. By generating recombinant refolded iNKT-cell TCRs, we show that natural single-nucleotide variations in iNKTα, translating to serine, threonine, asparagine or isoleucine at p93, exert a powerful effect on CD1d binding, with up to 28-fold differences in affinity between these variants. This effect was observed with CD1d loaded with either the artificial α-galactosylceramide antigens KRN7000 or OCH, or the endogenous glycolipid β-galactosylceramide, and its importance for autoreactive recognition of endogenous lipids was demonstrated by the binding of variant iNKT-cell TCR tetramers to cell surface expressed CD1d. The serine-containing variant showed the strongest CD1d binding, offering an explanation for its predominance in vivo. Complementary molecular dynamics modeling studies were consistent with an impact of p93 on the conformation of the CDR3α loop.
人类不变自然杀伤 T（NKT）细胞的 TCR 通过与 CD1d 结合的“不变” Vα24-Jα18 链（iNKTα）与半不变 Vβ11 链（iNKTβ）配对。在相当一部分人类 iNKT 细胞克隆（4-30%）中，已经报道了 iNKTα 位置 93（p93）的单个氨基酸变化，该位置位于“不变”CDR3α 区域的上游。尽管 p93 是大多数人类 iNKT 细胞 TCR 中的丝氨酸，与 CD1d 没有接触，但它可以通过改变关键 CDR3α 环的构象来影响 CD1d 的结合。通过生成重组重折叠的 iNKT 细胞 TCR，我们表明 iNKTα 中的天然单核苷酸变异，转化为 p93 处的丝氨酸、苏氨酸、天冬酰胺或异亮氨酸，对 CD1d 结合具有强大的影响，这些变体之间的亲和力差异高达 28 倍。这种效应在 CD1d 负载人工α-半乳糖基神经酰胺抗原 KRN7000 或 OCH 或内源性糖脂β-半乳糖基神经酰胺时都观察到，并且通过变体 iNKT 细胞 TCR 四聚体与细胞表面表达的 CD1d 的结合，证明了其对内源性脂质的自身反应性识别的重要性。含有丝氨酸的变体显示出最强的 CD1d 结合，为其在体内的优势提供了解释。互补的分子动力学建模研究与 p93 对 CDR3α 环构象的影响一致。
